It is planned to extend the application of the gas chromatographic mass spectrometric method for the determination of the primary structure of proteins to even larger molecules (greater than 250 amino acids long) than those previously investigated. The major objective is the design and development of the modifications of the present approach which will allow the speedy and reliable check of an amino acid sequence of a protein deduced from the base sequence of the gene which produces the protein. This work will be carried out using the enzyme alanine tRNA syntetase, a protein about 900 amino acids long. The most important modifications will involve methods for extracting mass spectral data on as many tetra-through hexapeptides as possible which are contained in the very complex peptide mixtures obtained from partial degradation of a protein (or protein segment) a few hundred amino acids long.